In the continuous casting of the metals such as brass or the like, it is common to permit molten metal to flow from a crucible through a die which is surrounded by a cooling apparatus so that the molten metal progressively solidifies and is intermittently withdrawn by a suitable apparatus. A major consideration in the efficiency of such an arrangement is the ability to remove heat from the die.
In my U.S. Pat. No. 4,285,388, an efficient apparatus for cooling the die is shown which utilizes a cooling sleeve having intimate contact with the exterior surface of the die, which cooling sleeve is cooled by flowing coolant about the periphery thereof. Inasmuch as the coolant comes into contact with the cooling sleeve which is cold and progressively increases in temperature, there is a tendency for the cooling sleeve to be cooled unevenly and expand out of contact with the die.
Where the product being cast is a strip or bar having an elongated cross section, it is very difficult to control the cooling so that the metal will solidify equally in a transverse direction with respect to the center line or longitudinal axis of the product being cast. When a conventional casting apparatus is used where the die is enclosed by a cooling sleeve there is a greater area of contact at the ends of the elongated cross section and the ends of the strip or bar being cast tend to solidify or freeze more rapidly than the center. As a result, the solidification or freezing line on the cast product tends to follow a negative sine curve. Accordingly, it has been found that it is necessary that the die must be very long in the direction of movement of the metal and the metal must be subjected to very slow cooling in order to provide reasonable quality at very slow production rates. Among the difficulties with such apparatus is that fractures tend to develop in the corners of the cast strip or bars, limiting the use of the product, and the fractures tend to become enlarged on further processing of the product.
When the casting is conducted by the movement of metal upwardly, known as up casting, the cooling sleeve and forming die are submerged in molten metal. As a result, more uniform cooling is required. As the cast product moves upwardly, the hot metal entering the die must move very rapidly in order to carry away sufficient heat to prevent remelting, must solidify in the shortest possible time and be strong enough to move away from the freezing zone in the die without fracturing the outer skin or surface of the product being cast. The solidification or freezing zone must be maintained horizontal with respect to the vertical direction of withdrawal of the product and the solidification must occur rapidly so that the product can be moved upwardly with minimum friction relative to the forming die.
Where the strip or bar is being cast vertically downwardly, known as down casting, the molten metal enters the die at the top and the ferrostatic pressure and heat of the molten metal tend to remelt the solidifying product at the end of each intermittent withdrawal stroke of the withdrawing apparatus. This results in this zone being only partly solidified transversely and moved to the next zone of the die. Thus, once again, the solidification or freezing zone of the product being cast should comprise a very narrow solidified band which is strong enough to be moved into the next zone of the forming die.
In casting of ingots where a greater mass of molten metal is to be cooled in the shortest possible time, a rapid cooling action is also required and a large amount of heat must be removed from the molten metal in the shortest period of time in order to produce a high quality ingot and a high rate of production.
It is therefore desirable to provide a construction for making such products which is capable of cooling all portions of the product uniformly to produce a substantially straight solidification or freezing line transversely of the axis or direction of movement of the product through the die. Otherwise, any portions that solidify at a later time in the movement of the metal may result in point of incipient leaking through of the eutectics of the alloy which have a lower melting point than the remainder of the alloy producing exudation or beads on the surface of the cast product. Such eutectics tend to pierce the surface of the strip or bar being cast and, as the piercing continues, molten metal flows through the apertures that have been formed carrying with it a volume of heat which, in turn, melts the outer surface of the product being cast and eventually results in interruption in the casting operation.
Accordingly, among the objectives of the present invention are to provide a continuous casting apparatus for casting products which have an elongated cross section wherein the freezing line on the finished product is substantially transverse to the axis of the product; wherein the apparatus can be adjusted to accommodate changes in the product being cast or the molten temperature; and wherein the structure is economical to construct and operate.
In accordance with the invention, the continuous casting apparatus comprises a graphite die having an opening therethrough which has an elongated cross section and a cooler body surrounding and supporting the die. One of the graphite die and body has a plurality of axially extending coolant passages in transversely spaced relation along each of the long sides of the elongated opening. Each coolant passage has an inlet end and an outlet end and the length of the coolant passages decreases progressively from the passage nearest the center to the end of the elongated openings.